In known drilling systems of this kind, the drill bit may be driven by a motor receiving power by way of the drilling mud supplied to the drilling site, or by an electric motor. Difficulties are encountered with electric motor drive arrangements because of the length of the necessary cable connection, and the adverse environment in which the electric motor has to operate. Further problems arise in connection with directional or horizontal drilling, because information relating to performance of the drill bit and to its position has to be conveyed along the drill string more or less continuously. Mud pulsing can be employed in the mud drilling systems but the speed of data transmission is low, as is the volume of data that can be transmitted.
It is accordingly an object of the present invention to provide a drill string for a drilling system which facilitates transmission of electric power supply and/or communication signals therealong.
It is also an object of the invention to provide a drill string structure providing inbuilt electrical conductor means, in sections which can be handled by conventional pipe handling equipment.
It is also an object of the invention to provide a drill string structure having facilities therein for transmission of electric power and/or communication signals, for supply of drilling mud and for supply and/or return of protective or other fluid.
It is also an object of the invention to provide a drill string for use in a drilling system having selectively operable means for advancing the drill string along a drill hole in particular, a non-vertical drill hole.
It is also an object of the invention to provide a drill string which can be moved relative to a drill hole wall.
It is also an object of the invention to provide a drill system in which drilling reaction forces can be transferred to the drill hole wall.
It is also an object of the invention to provide a drill system incorporating remotely controllable local power generators at desired positions within the system.
It is also an object of the invention to provide a drill unit of which the drill bit can be selectively loaded in the drilling direction.
It is also an object of the invention to provide a drill unit of which the drilling direction can be selectively angled with respect to a drill hole axis.